Apart they're just 7 magic balls. But if you find them and bring them
together, they summon the Eternal Dragon who rises from his lair in a fury
of ageless wonder and grants a wish to the person that awoke the dragon
from his slumber.

Yep. That's pretty much what the Dragon Balls are. And what would DBZ be
without the DragonBalls? There wouldn't be any power hungry enemies trying
to gain immortality, and DBZ would simply not be...umm...DBZ! Oh, but
theres more to these seven, spherical mystical balls than meets the eye!
There are in fact 3 different 'sets' of Dragon Balls in Dragon Ball Z.
These sets are :

Earth Dragon Balls : Kami's

Name of Dragon : Shenron (Shenlong)
How to Wake the Dragon : Shout out 'Come out Shenron'. All balls must be gathered on same spot.
Wishes : 1
Size : Can fit in the palm of your hand.
How they were created : Mr Popo made a model of a Dragon and asked Kami to make it come to life. Kami made it come to life and created the Dragon Balls with it. He wanted humans to have something to work towards in life. But when evil people started to crave for the DBs to grant their wishes, in
was only when people like Goku turned up that he knew what he had created
the DBs for.
Properties/Limitations :
Only one wish to be granted.
After the wish is made, balls turn to stone and spread out. After 1 year, the
balls become active as Dragon Balls again.
The wish cannot exceed Kami's power.
You cannot wish to be in love with someone or to kill someone.
You revive the same person only ONCE.
You cannot revive someone who died of natural causes.
You can revive any number of people as long as they died for the same reason.

Earth Dragon Balls : Dende's

Exactly the same as Kami's Dragon Balls but...

2 wishes can be granted (3 are granted in the Buu Saga because Dende powers
them up).

Namek Dragon Balls

Name of Dragon : Porunga
How to Wake the Dragon : 'Takkarapto Popporunga Pupiritto Paro' (Namekian)
Wishes : 3
Size : Huge. You need both hands (and arms!) to hold just one.
How they were created : Guru created these Dragon Balls, and as far as I
know, they were created in the same way that Kami made them (by using a
model of a Dragon).
Properties/Limitations : Only 3 wishes. After the wishes are made, the balls
turn to stone and scatter themselves. They return to become Dragon Balls
after 1 Namek year (130 Earth days).You cannot wish to destruct someone or
fall in love with someone.Porunga can revive any person any amount of times.